The Los Angeles Reservoir needed some shade, so the Los Angeles Department of Water and Power (LADWP) released 96 million, 102-mm (4-in.), black plastic balls — nicknamed shade balls — into the water.

By blocking sunlight from much of the 70.8-ha (175-ac) reservoir, the shade balls are helping LADWP comply with U.S. Environmental Protection Agency water quality requirements. Sunlight can cause chemical reactions that result in algae blooms and other environmental exposures. In addition, this strategy is saving LADWP more than $250 million and 1.1 billion L (300 million gal) of water each year, which had previously been lost to evaporation, according to an LADWP fact sheet.

The shade balls block sunlight to help reduce algae blooms and improve water quality. Photo courtesy of the Los Angeles Department of Water and Power.

Because of the reservoir’s large size, using a single floating protective cover to meet standards would not have worked. Two floating covers would have cost more than $300 million for installation and an additional $100 million in operational adjustments. The shade balls, weighed down with water inside, cost $34.5 million to deploy and achieve the same water quality results. They also have a 10-year lifespan and require no construction, labor, or maintenance, the fact sheet says.

Shade balls have been in use at other LADWP open-air reservoirs since 2008 and have been confirmed to be effective in protecting water quality. Using shade balls also is expected to greatly reduce the Los Angeles Reservoir’s daily chlorine requirement and save about $28,000 a month in current chlorine costs, the fact sheet says.